The code is mostly derived from cx_bsdiff (written by Anthony Tuininga,
http://cx-bsdiff.sourceforge.net/). The cx_bsdiff code in turn was derived
from bsdiff, the standalone utility produced for BSD which can be found
at http://www.daemonology.net/bsdiff.
In addition to the two functions (diff and patch) cx_bsdiff provides, this
package includes:

an interface to the BSDIFF4-format

command line interfaces: bsdiff4 and bspatch4

tests

The bsdiff4 package defines the following high level functions:

diff(src_bytes, dst_bytes) -> bytes

Return a BSDIFF4-format patch (from src_bytes to dst_bytes) as
bytes.

patch(src_bytes, patch_bytes) -> bytes

Apply the BSDIFF4-format patch_bytes to src_bytes and return
the bytes.

file_diff(src_path, dst_path, patch_path)

Write a BSDIFF4-format patch (from the file src_path to the
file dst_path) to the file patch_path.

file_patch(src_path, dst_path, patch_path)

Apply the BSDIFF4-format file patch_path to the file src_path
and write the result to the file dst_path.